Patterned conductor leads are used in a semiconductor device such as an integrated circuit in a variety of ways such as grounding wire, power supply conductor, signal conductor, etc. The width of such patterned conductor leads is varied corresponding to the respective use. Accordingly, a plurality of conductor leads having varied widths are formed in the same conductor lead layer. On the other hand, the height of each patterned conductor lead is the same value determined by the film thickness formed for each conductor lead. Thus, a large difference arises in the ratio of height to width of the conductor leads, i.e., the aspect ratio of patterned conductor leads formed in the same layer.
FIG. 14 is a sectional view of conventional patterned conductor leads disclosed in page 5 of "Advanced Metallization for VLSI Applications in 1993". In the drawing, transistors 1 are formed on a Si substrate, and interlayer insulating films 4 composed of SiO.sub.2 are disposed. Then, a first conductor lead layer 2 is formed, in which a principal conductor material 7 such as AlSi and an adhesion layer 8 such as TiN are laminated. This layer is formed by successive sputtering of lead material on the interlayer insulating film 4, followed by reactive ion etching (RIE) via a resist mask thereon. Then, a further interlayer film 4 may be formed thereon, and a second conductor lead layer 3 may be formed similarly. It is possible to further stack a conductor lead layer thereon.
Conductor leads in the first conductor lead layer 2 have the same height and different width, therefore an aspect ratio (i.e, ratio of height to width) of each conductor lead is quite different. The difference in aspect ratio occurs likewise among the conductor leads in the second conductor lead layer 3. It is difficult to etch the patterned conductor lead material in the same depth by reactive ion etching (because of such a large difference in aspect ratio) . Thus, deficient etching and short-circuit between patterned conductor leads results.
Recently, a method for forming patterned conductor leads was proposed in which patterned grooves were filled with conductor lead material (i.e., buried conductor leads). FIG. 15 is a sectional view of another conventional conductor lead shown on page 39 of the 41st VLSI FORUM titled "Wiring Technique of High Speed Processing Device" (Japanese publication). In the drawings, transistors 1 are formed on a Si substrate, and an interlayer insulating film 4, generally composed on Sio.sub.2, is disposed thereon. Then, an etching stopper 14, generally composed of SiN, is formed. When grooves are formed in an interlayer insulating material 4, etching is substantially stopped by the etching stopper 14. In a first conductor lead layer 2, an adhesion layer 8, such as TiN, is formed with good coverage. Next, the grooves are filled with principal conductor material 7, such as AlSi. Then, the conductor lead materials formed outside the groove portions are removed, whereby the patterned conductor leads are formed. In this conventional process, since the etching stopper of insulating film is formed, depth of the grooves is constant. Accordingly, the aspect ratio of the patterned conductor leads formed in the same conductor lead layer are largely different.
In the manufacturing method of the conventional buried conductor leads, etching rate or etching speed is substantially constant irrespective of the width of grooves, and as a result, the aspect ratio of the formed conductor leads is largely different. FIG. 16 shows a relation between the width of the groove and the etching rates. The SiO.sub.2 layer is etched by RIE using CHF.sub.3 (of 30 sccm in flow rate) as an etching gas, and AR (of 30 sccm in flow rate) and O.sub.2 (of 5 sccm in flow rate) mixed gas as an additive gas. It is understood from the drawing that the etching rate is substantially constant irrespective of the groove width. Because of large differences in the aspect ratio of conventional buried conductor leads, it is difficult to bury conductor lead material in deep grooves, resulting in deficient burying and defective conductor leads.
Therefore, the width of conductor leads formed in the same conductor lead layer are limited to a small range depending on the film thickness of the conductor leads. As a result, it is impossible to form conductor leads having a large variety of width in the same conductor lead layer. Alternatively, the film thickness of the conductor leads can not be increased in a conductor lead layer where fine conductor leads are formed.